The present invention relates generally to self-aligned pattern formation. More particularly, the present invention relates to self-aligned pattern formation using dual wavelengths to achieve smaller resolution than is achievable by conventional ultraviolet (UV) lithography.
The semiconductor or IC industry aims to manufacture integrated circuits (ICs) with higher and higher densities of devices on a smaller chip area to achieve greater functionality and to reduce manufacturing costs. This desire for large scale integration has led to a continued shrinking of circuit dimensions and device features. The ability to reduce the size of structures, such as, gate lengths in field-effect transistors and the width of conductive lines, is driven by lithographic performance.
Semiconductor fabrication techniques often utilize a photomask (also referred to as a mask) or a reticle. Radiation is provided through or reflected off the mask or reticule to form an image on a semiconductor wafer. Generally, the image is focused on the wafer to pattern a layer of material, such as, photoresist material. In turn, the photoresist material is utilized to define doping regions, deposition regions, etching regions, or other structures associated with integrated circuits (ICs). The photoresist material can also define conductive lines or conductive pads associated with metal layers of an integrated circuit. Further, the photoresist material can define isolation regions, transistor gates, or other transistor structures and elements.
To transfer an image or pattern onto the photoresist material, a conventional lithographic system generally includes a light source configured to provide electromagnetic radiation or light at one or more wavelengths. The light source may produce radiation at a wavelength of 365 nanometers (nm), 248 nm, and/or 193 nm. The photoresist material patterned by such radiation is selected to be responsive at the wavelength of such radiation. Preferably, the areas of the photoresist material upon which radiation is incident undergo a photochemical change such that it becomes suitably soluble or insoluble in a subsequent developing process step.
Because the resolution of features is, in part, proportional to the exposure wavelength, it is desirable to pattern photoresist material using shorter exposure wavelengths (e.g., 157 nm, 126 nm, or 13.4 nm). Unfortunately, few, if any, materials or processes can consistently fabricate semiconductor integrated devices at such shorter wavelengths. Attempts to use conventional photoresist materials, such as organic based photoresist materials, used in 365 nm, 248 nm, or 193 nm lithographic systems are not without problems. Organic based photoresist materials exhibit high optical absorption per unit thickness in single layer patterning applications at the shorter lithographic or exposure wavelengths. Thus, conventional organic based photoresist materials become increasingly opaque to the exposing radiation and the necessary photochemical change does not occur throughout the entire thickness of the material.
To overcome this drawback, a thinner layer of conventional photoresist material (relative to the thickness used in longer wavelength lithography) has been tried with shorter lithographic wavelengths. Unfortunately, the use of a thinner layer of photoresist material is problematic especially during etch processing. Among others, using a thinner layer results in low pattern fidelity, thin film instability problems, and/or inadequate imaging performance.
Thus, there is a need for a system and method for effectively extending the use of conventional photoresist materials to shorter lithographic wavelengths in the deep ultraviolet (DUV) or extreme ultraviolet (EUV) range. There is a further need for a system and method of pattern formation that achieves the feature resolutions of shorter lithographic wavelengths without extensive modifications to conventional lithographic techniques, materials, or equipment. Even further still, there is a need for a process or method that provides pattern self alignment and obviates the need for mask overlay.
An exemplary embodiment relates to an integrated circuit fabrication process. The process includes exposing a photoresist material provided over a substrate to a first radiation at a first lithographic wavelength, and selectively transforming a top portion of the photoresist material in accordance with a pattern provided on a mask or reticule. The process further includes exposing the photoresist material to a second radiation at a second lithographic wavelength. The first lithographic wavelength is smaller than the second lithographic wavelength. The transformed top portion of the photoresist material is non-transparent to the second radiation.
Another exemplary embodiment relates to an integrated circuit fabrication system. The system comprises a first light source providing a first radiation at a first lithographic wavelength, and a second light source providing a second radiation at a second lithographic wavelength. The system further includes a self-aligned mask included in a photoresist layer. The self-aligned mask is formed by exposure to the first radiation at the first lithographic wavelength in accordance with a patterned mask or reticule.
Still another exemplary embodiment relates to a method of extending the use of currently available DUV-248 nm and DUV-193 nm photoresists to 157 nm, 127 nm, and 13.4 nm lithographic regimes. The method includes providing a first radiation at a short lithographic wavelength. The method further includes transforming a top portion of a photoresist layer provided over a substrate in accordance with a pattern on a mask or reticule. The transformed top portion of the photoresist layer includes at least one polymerized area where the first radiation is incident thereon. The transformed top portion comprises the pattern from the mask or reticle.